a) Field of the Invention
The invention is directed to a process and a device for detecting physical, chemical, biological or biochemical reactions and interactions on biochemically or chemically functionalized specimen carriers in the form of layers or films from the spectral reflection after irradiation with light of different wavelengths. It is based on the resonance phenomenon excited by evanescent fields in planar waveguides and in thin metal films which react to changes in or attachment to the biosensitive film located thereon as well as on interference phenomena occurring as the result of reflection at the interfaces or boundary surfaces of this film.
b) Description of the Related Art
WO 93/14392 discloses a device for detecting such reactions and interactions in which collimated, polychromatic light is totally reflected at an internal prism surface. Given a suitable selection of the parameters of a spacing layer film and a cavity layer located above the latter, the occurring evanescent field is coupled into the cavity layer at resonance, wherein the resonance is effected in different wavelengths depending on the specimen interaction above the cavity layer. In a subsequent wavelength-dispersive unit, the resonance wavelength is determined as an extreme value in the spectrum.
Another arrangement for detecting biochemical interactions is known from EP 0 257 955. In this case also, polychromatic light is coupled into a transparent plate via a multiple-prism structure and is totally reflected at the transparent plate at an angle of incidence greater than the critical angle. The vertically oscillating polarization component of the evanescent field excites collective electron density oscillations (surface plasmons) in a thin metal film applied to the boundary surface. This resonance phenomenon is influenced by changes at the boundary surface due to the morphology or nature of the specimen and is detected as absorption of the respective resonance wavelength in a subsequently arranged dispersive device. The changes at the boundary surface owing to the nature of the specimen accordingly result in a shifting of the reflection minimum which is a criterion for the nature of the analyzed specimen.
WO 93/01487 describes an arrangement for the selective detection of substances in chemical, biochemical and biological measurement specimens by determining changes in the effective refractive index of a guided mode by means of a grating coupler. The grating coupler is arranged on a transparent substrate plate in the boundary surface interfacing with an applied planar waveguide and takes over the functions of input coupling and output coupling of radiation. The coupling efficiency of the entire arrangement depends upon the polarization, the angle of incidence, the waveguide characteristics, the grating characteristics, and the refractive index above the waveguide. In the input coupling optimum, a mode is excited in the waveguide and, at a determined coupling angle, the reflectivity of the grating coupler achieves a minimum which is recorded by a position-sensitive detector.
DE 42 00 088 discloses a process and a device for detecting physical, chemical, biochemical and biological processes, wherein light of a suitable wavelength or of a suitable spectral range is radiated into a specimen at which the process takes place at or in at least one thin layer of at least partially optically transparent material. In so doing, the interference phenomena which are brought about as a result of the process are detected and measured and can be interpreted and represented as a change in the optical layer thickness. For this purpose, the absolute optical layer thickness can be calculated from the spectral position of the interference extrema and their distance from one another. The optical layer thickness can also be determined from the change in intensity in one or more wavelengths. A device for carrying out the process comprises a light source emitting white light, a specimen arrangement at which the process to be studied can be carried out, a detector, for example, a photoelectric receiver array, and an evaluating device, e.g., a computer. The specimen arrangement has a base with a carrier layer comprising a thin polymer film (e.g., polysiloxane film) in which the process to be detected takes place. The base can be a glass plate, a commercially available interference filter or a suitable substrate.
All of these devices have the disadvantage that they can only be used to carry out individual measurements. The simultaneous measurement of a plurality of specimens would substantially increase technical complexity. It would only be possible to expand these measurements to a few parallel measurement objects and specimens. An example of such a device, by means of which four specimens can be measured, is described and shown in WO 93125 909.
A further disadvantage consists in that in arrangements with an angle-selective light radiation or coupling in of radiation, converting to the simultaneous measurement of a plurality of specimens requires costly duplication of the coupling structure as is illustrated in WO 92/0542.